In recent years, reduction in rolling resistance of a pneumatic tire has been sought in order to improve the fuel economy of a vehicle on which the pneumatic tire is mounted and to improve the maximum speed of the vehicle. In order to reduce the rolling resistance of the pneumatic tire, various aspects in which the construction of the pneumatic tire, the tread pattern design, and the like are changed have been proposed.
Also, in order to improve the fuel economy of the vehicle and to improve the maximum speed of the vehicle, reducing the air resistance of the pneumatic tire during rolling motion has been proposed. The air resistance of the pneumatic tire is affected by concave and convex of a tread pattern provided on a tread portion surface and by concave and convex in markings and a pattern provided on a sidewall surface.
For example, a pneumatic tire is known that has no spew or cut traces of spew on the sidewall surface and is able to reduce air resistance (see Japanese Unexamined Patent Application Publication No. 2012-106583A).
A first region in the sidewall surface of such a pneumatic tire includes a maximum tire width position and is provided with a plurality of recesses shaped as dimples. A serration process is applied around each of the recesses to provide a plurality of trough portions shaped as lines extending unidirectionally to enclose the recesses.
The above-described pneumatic tire is provided with a plurality of recesses shaped as dimples in a region that includes the maximum tire width position on the sidewall surface of the tire. Thus, it is possible to reduce air resistance produced during the rolling motion of the pneumatic tire, which is effective in improving the fuel economy.
Conversely, in order to achieve a reduction in weight and low rolling resistance for the pneumatic tire, the thickness of the sidewall (hereinafter, also referred to as side gauge) is made thinner. However, making the side gauge thinner tends to produce appearance defects in the sidewall surface with high probability. Such appearance defects have no negative effect on tire durability or on maneuverability, yet cause a user to suspect that the tire is of low quality in terms of durability and maneuverability. Specifically, in a molding process during tire manufacture, a carcass member shaped as a sheet is wound once over a tire molding drum. A winding starting end and a winding finishing end of the carcass member partially overlap to form a joint. Therefore, the thickness is greater at this overlapping portion. This portion ultimately appears as undulations in the sidewall surface of the finished tire. Specifically, such undulations are remarkable in a radial tire using one carcass member.
In a pneumatic tire provided with the plurality of recesses shaped as dimples on the sidewall surface, as described above, providing the plurality of dimples serves to make the undulations actually appearing in the sidewall surface more difficult to notice. Making the undulations less noticeable is sought.